Keisen Air Quality Index (AQI)

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Keisen, nestled within Fukuoka Prefecture on the island of Kyushu, Japan, presents a unique geographic setting influencing its air quality. The city occupies a relatively flat coastal plain, situated at a low elevation near Hakata Bay, a significant inlet of the Sea of Japan. This proximity to the sea introduces maritime influences, moderating temperatures but also potentially trapping pollutants during stable atmospheric conditions. Keisen isn’t heavily industrialised itself, but benefits from, and is impacted by, the larger industrial concentration around Fukuoka City to the east. Surrounding Keisen are agricultural lands, primarily rice paddies and vegetable farms, which contribute to background levels of ammonia and particulate matter from agricultural practices. The urban-rural gradient is relatively sharp; moving inland quickly transitions from residential areas to more rural landscapes. The terrain is largely composed of alluvial deposits, making the area susceptible to localised flooding which can redistribute pollutants. The city’s position within a valley-like formation, shielded by hills to the south, can exacerbate pollution build-up, particularly during temperature inversions. This geographical configuration, combined with prevailing wind patterns, dictates how pollutants disperse – or concentrate – within the urban environment, impacting respiratory health and overall air quality.

Keisen’s air quality follows a distinct seasonal pattern. Spring (March-May) often sees increased pollen counts, impacting those with allergies, alongside moderate particulate matter from dust storms originating from the Asian continent. Summer (June-August) brings the humid subtropical climate into full force, with the Tsuyu (rainy season) initially offering some cleansing effect, washing pollutants from the atmosphere. However, stagnant air during breaks in the rain can lead to localised build-up of ozone due to increased sunlight and vehicle emissions. Autumn (September-November) is generally the clearest period, with cooler temperatures and stronger winds aiding dispersion. However, the tail end of typhoon season can bring periods of high humidity and potential for pollutant re-suspension. Winter (December-February) is often the most challenging time. Siberian air masses bring cold, dry air, and temperature inversions are frequent, trapping pollutants near the ground. Reduced sunlight limits photochemical reactions that break down pollutants. Sensitive individuals – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during these winter months. Monitoring wind direction is crucial, as pollutants can accumulate quickly when winds are light and from the industrial areas to the east.